Components that are subjected to considerable loading, such as turbine blades for instance, undergo high thermal and mechanical stress during operation, possibly leading to instances of material fatigue and as a consequence to cracks. Since the production of components which are exposed to a very high temperature during operation, such as for example components of a gas turbine, is relatively costly, it is generally endeavored to repair such components when they are damaged. This makes the component serviceable again and allows it to be used for a further period between inspections.
Furthermore, nowadays materials which have an oriented microstructure instead of a polycrystalline structure are being increasingly used for producing components of turbines, since these materials have better material properties, in particular in the high temperature range. The repair of such components is nevertheless made more difficult by the fact that during heat treatment of the material there is the risk of the repaired location no longer having an oriented microstructure.
One possible way of repairing damaged components is, for example, welding. However, welding methods should be avoided when repairing components that are subjected to considerable loading, in particular those which have an oriented structure, since they melt the base material of the component. Therefore, structurally bearing regions of a component must not be welded, since the integrity of the oriented structure would be lost as a result of the melting of the base material.
A further possible way of repairing damaged components is soldering. In the case of the conventional soldering methods, a solder is applied to the base material in the region of the damage and bonded to the base material by means of exposure to heat. However, in the case of the previously customary procedure, after the soldering the soldered location has inferior material properties than the surrounding base material, for example it does not have an oriented microstructure.
US 2004/0050913 describes a further method of repairing a component of a gas turbine by means of a solder with nanoparticles dispersed in a carrier liquid. The solder is applied to the cleaned surface of the location to be repaired and the component is heat-treated for four hours at a temperature of approximately 2120° F. (1433 K) in a vacuum of 0.3 Pa, the temperature increase being maintained for 10 minutes at approximately 800° F. (700 K) and 1600° F. (1144 K). Subsequently, the temperature is reduced by means of an inert gas, maintained for 20 minutes at 1000° F. (811 K) and then the component is cooled to room temperature. During the heat treatment, the nanoparticles melt at a temperature which is significantly lower than the melting temperature of the microparticles that are usually used in soldering. This dispenses with the need to add agents which lower the melting point, which have to be added in the case of most soldering methods for repairing gas turbines and which impair the material properties of the repaired location.